Autonomous Mobile Robot Design - Autonomous Robots Lab...Autonomous Mobile Robot Design Dr. Kostas...

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Autonomous Mobile Robot Design Dr. Kostas Alexis (CSE) Topic: Propulsion Systems for Robotics

Transcript of Autonomous Mobile Robot Design - Autonomous Robots Lab...Autonomous Mobile Robot Design Dr. Kostas...

Page 1: Autonomous Mobile Robot Design - Autonomous Robots Lab...Autonomous Mobile Robot Design Dr. Kostas Alexis (CSE) Topic: Propulsion Systems for Robotics. Propulsion Systems for Robotics

Autonomous Mobile Robot Design

Dr. Kostas Alexis (CSE)

Topic: Propulsion Systems for Robotics

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Propulsion Systems for Robotics

How do I move?

Understanding propulsion systems is about knowing how

a mobile robot can actuate it, how it generates the

required forces for its motion.

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Propulsion Systems for Robotics

Different propulsion systems designs are employed

for different robotic configurations.

Miniaturization of propulsion systems –in

combination with good efficiency– is among the

reasons for the success of small robotics.

Within this course we will focus on:

DC Motors

DC Brushless Motors

Propelled-systems

Wheeled-systems

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Our focus

Design of Propelled Aerial Robots and Wheeled Ground Robots

Many other interesting robot configurations also exist!

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DC Motors

Stationary permanent magnet

Electromagnet on axis induces torque

Split ring + brushes switch direction of current

If you have never built one – do so!

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Control of DC Motors

More power means faster rotation

How to modulate power using a digital

signal? What is the digital equivalent function

to directly control power at the input?

Fixed voltage with pulse modulation –

specifically:

Pulse Width Modulation (PWM)

Duty cycle is the proportion of “ON” time vs.

period

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Brushless Motors

Electromagnets are stationary

Permanent magnets on the axis (either inside or

outside)

Three coils (or more)

No brushes (less maintenance, higher efficiency)

Brushless motors come with high torque, mostly

eliminating the need for gearboxes in case of

multirotor aerial robots therefore maximizing

endurance

https://www.hobbyking.com/hobbyking/store/

__25556__AX_2810Q_750KV_Brushless_Quadcopter_Moto

r.html

www.mpoweruk.com

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Brushless Electronic Speed Controllers

Typically one microcontroller per motor

Called Electronic Speed Controller (ESC)

Generates PWM signal for the three motor phases

AC signal converter (MOSFET) to convert PWM to

analogue output

Measure motor position/speed using back-EMF

http://en.wikipedia.org/wiki/File:ESC_35A.jpg

A-B

B-C

C-A

A

BC

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I2C Protocol

Often digital protocol to command the ESC

Serial data line (SDA) + serial clock line (SCL)

All devices connected in parallel

7-10 bit address, 100-3400 kbit/s speed

Communication between motor controller and autopilot

http://en.wikipedia.org/wiki/File:I2C.svg

http://en.wikipedia.org/wiki/File:I2C_data_transfer.svg

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The Micro Aerial Vehicle propeller

Is something much simpler than a helicopter rotor

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The Micro Aerial Vehicle propeller

Video of airflow and vortex patterns with propellers. These tests were conducted at NACA, nowNASA Langley Research Center. The interior tests were probably at the Propeller Research Tunnel.The exterior tests at the end of the film were at the Helicopter Test Tower. Langley Film #L-118

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The Micro Aerial Vehicle propeller

Rotor modeling is a very complicated process.

A Rotor is different than a propeller. It is not-rigid

and contains degrees of freedom. Among them

blade flapping allows the control of the rotor tip

path plane and therefore control the helicopter.

Used to produce lift anddirectional control.

Elastic element between bladeand shaft.

Blade flapping used to changetip path plane.

Blade pitch angle controlled byswashplate.

Used to produce thrust.

Propeller planeperpendicular to shaft.

Rigid blade. No flapping.

Fixed blade pitch angle orcollective changes only.

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The Micro Aerial Vehicle propeller

In a simplified assumption, a propeller is

considered to present no blade flapping.

It is approximated as a rotor disc producing thrust

and drag forces.

Thrust & Power Equations

Hover case (ideal power):

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The Micro Aerial Vehicle propeller

Thrust & Power Equations

Hover case (ideal power):

Figure of Merit:

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The Micro Aerial Vehicle propeller

Lift & Drag at Blade Element:

A0: zero lift angle of attack.

Linearize polar for Reynolds number at 2/3 R

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The Micro Aerial Vehicle propeller

Simplified model forces and moments:

Thrust Force: the resultant of the vertical forces acting on

all the blade elements.

Hub Force: the resultant of all the horizontal forces acting

on all the blade elements.

Drag Moment: This moment about the rotor shaft is

caused by the aerodynamic forces acting on the blade

elements. The horizontal forces acting on the rotor are

multiplied by the moment arm and integrated over the

rotor. Drag moment determines the power required to

spin the rotor.

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The wheel of a small ground robot

Circular Motion – Rotational Formulas

Angular Velocity

Angular Velocity and Acceleration

Angular Displacement

Angular Acceleration

Angular Momentum or Torque

ω = angular velocity

θ = angular position

r = radius of the wheel

a = angular acceleration

Jw = moment inertia

T = angular momentum

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Code Example

MATLAB DC Motor Control Example

https://github.com/unr-arl/autonomous_mobile_robot_design_course/tree/master/matlab/propulsion-systems/motor-

control

MATLAB 2016 Live note

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Code Example

Indicative in-class run

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How does this apply to my project?

DC Brushless Motors with Electronic Speed Controllers are used for the

actuation of the multirotor UAVs, the fixed-wing UAV and the remote-

controlled boat of the course projects.

DC brushed motors are used for the actuation of the ground robot of the

course projects.

What do I have to do about it?

Not much. The on-board autopilot you are integrating is handling such basic

functionalities.

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Thank you! Please ask your question!